1. Field of the Invention
Embodiments of the invention generally relate to a fabrication process for depositing a barrier layer on a substrate, and more particularly to a deposition and densification process for forming a titanium nitride barrier material.
2. Description of the Related Art
Reliably producing submicron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) of semiconductor devices. However, as the fringes of circuit technology are pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology have placed additional demands on the processing capabilities. The multilevel interconnects that lie at the heart of this technology require precise processing of high aspect ratio features, such as vias and other interconnects. Reliable formation of these interconnects is very important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates.
As circuit densities increase, the widths of interconnects, such as vias, trenches, contacts, and other features, as well as the dielectric materials between, decrease to 45 nm and 32 nm dimensions, whereas the thickness of the dielectric layers remain substantially constant, with the result of increasing the aspect ratios of the features. Many traditional deposition processes have difficulty filling submicron structures where the aspect ratio exceeds 4:1. Therefore, there is a great amount of ongoing effort being directed at the formation of substantially void-free and seam-free submicron features having high aspect ratios.
In the manufacture of integrated circuits, a titanium/titanium nitride stack, a titanium nitride layer over a titanium layer, is often used as a liner barrier. The titanium/titanium nitride stack may be used to provide contacts to the source and drain of a transistor. In one example, a titanium layer may be deposited over a silicon substrate. The titanium nitride layer may be deposited over the titanium layer. The titanium nitride layer may be used as a barrier layer to inhibit the diffusion of metals into regions underlying the barrier layer. A conductive metal layer, such as a copper-containing layer or a tungsten-containing layer, is usually deposited over the titanium nitride layer.
The titanium layer or the titanium nitride layer may be formed by a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, and/or a physical vapor deposition (PVD) process. For example, the titanium layer may be formed by reacting titanium tetrachloride with a reducing agent during a CVD process and the titanium nitride layer may be formed by reacting titanium tetrachloride with ammonia during a CVD process. Thereafter, the conductive material may be deposited onto the substrate.
A variety of problems that eventually may lead to device failure is a result from the specific process used to deposit or form the titanium nitride layer. Reliability problems may occur from the use of titanium tetrachloride as a chemical precursor to form a titanium nitride layer during a CVD process. In particular, the titanium nitride layer may have poor adhesion over the titanium layer, resulting in peeling of the titanium nitride layer from the titanium layer. Another problem arises since the titanium tetrachloride precursor produces chlorine which diffuses and contaminates neighboring materials (e.g., dielectric or conductive) on the substrate.
Titanium nitride barrier layers deposited with a traditional CVD process further endure the severe problem of the conductive contact material (e.g., Cu, W, or Al) diffusing through the barrier layer and into neighboring materials, such as dielectric materials. Often, this diffusion problem occurs because the barrier layer is too thin or contains a barrier material not dense enough (e.g., too porous) to prohibit or limit the diffusing metallic atoms. Thicker barrier layers may be used to limit or control diffusion. However, the resistance of a barrier layer increases proportional to the thickness, as does the time and cost for deposition.
Therefore, there is a need for an improved method of depositing and densifying barrier materials, particularly titanium nitride barrier layers.